1. Field of the Invention
The present invention relates to a control device and a control method for an electrically driven vehicle including an electric vehicle (EV) and a hybrid electric vehicle (HEV), and more particularly, to a failure of a coolant temperature sensor.
2. Description of the Related Art
In recent years, hybrid vehicles and electric vehicles are attracting attention as vehicles intended for energy saving and environmental friendliness. The hybrid vehicle has a motor as its power source in addition to a related-art engine, and the electric vehicle has a motor as its power source.
Both the hybrid vehicle and the electric vehicle are configured to use an inverter circuit to invert DC power stored in a battery to AC power to drive a motor and travel.
The inverter circuit is constructed by switching devices such as insulated gate bipolar transistors (IGBTs) or field effect transistors (FETs), and applies on/off control to the switching devices, thereby inverting the DC power to the AC power.
On this occasion, a current flows when the switching device is turned on, and as a result, the temperature of the switching device increases. Therefore, a temperature sensor configured to measure switching device temperature is provided to limit the current flowing through the switching device so that the switching device temperature does not exceed a limit and the switching device is protected from breakage.
As an example of the above-mentioned configuration, according to Japanese Patent Application Laid-open No. Hei 10-210790, an inverter electronic control unit (ECU) is configured to control an inverter to drive a motor, and detect an inverter temperature based on input from an inverter temperature sensor. Then, when the inverter temperature drastically increases, the inverter ECU adjusts a torque command value directed to the inverter, that is, suppresses an output torque of the motor to decrease a heat generation amount of the switching devices, thereby protecting the switching devices.
However, the technology described in Japanese Patent Application Laid-open No. Hei 10-210790 does not consider a case where a coolant temperature sensor has failed. Thus, in a case where the coolant temperature sensor has failed, and as a result, the actual coolant temperature becomes unknown, there occurs no problem when a cooling system is normal, while when the cooling system is brought into an abnormal state by leakage of the coolant or a failure of a water pump, the coolant temperature abnormally increases, and the generated heat of the switching devices is difficult to be absorbed by the coolant. As a result, the output torque suppression for the motor that is set assuming that the cooling system is normal, that is, the coolant temperature is normal, may not protect the switching devices from breakage.
Moreover, a method involving immediately stopping the motor drive when the failure of the coolant temperature sensor is detected so as to protect the switching device is conceivable, but this method has such a problem that the vehicle may become unable to travel in vain when the cooling system is not abnormal.